This invention relates to kidney dialysis, and provides an improved filter system for home use dialysis procedures.
When a person""s kidney function is about three percent (3%) of normal, the person is said to have end stage renal disease (ESRD). Continuous ambulatory peritoneal dialysis (CAPD) is a medical therapy used to remove the toxins that accumulate in the blood when the kidneys stop functioning. Peritoneal dialysis uses the person""s peritoneal lining as a filter mechanism. The patient introduces dialysis solution into the peritoneal cavity through a surgically implanted catheter. To accomplish this form of dialysis, the patient leaves the solution in his or her peritoneal cavity for about 4 hours and then drains the solution out of the peritoneal cavity. During the time the dialysis solution is in the patient""s peritoneum, the toxins in the patients blood streem diffuse through the peritoneal lining into the dialysis solution. When the solution is drained, the toxins are flushed from the peritoneum with the fluid. After draining the fluid, the patient repeats the procedure by again introducing fresh sterile solution into the peritoneal cavity to continuously remove toxins from the blood. The patient transfers the solution in and out of the peritoneal cavity 4 or more times per day. Currently, most patients transfer about 4 times per day.
There are several problems associated with using CAPD to treat ESRD. The main drawback is the increased risk of peritonitis. Peritonitis may be caused by infectious bacteria getting into the peritoneal cavity from the environment Other causes of peritonitis infection include organic matter entering the peritoneal cavity from the environment or non-dissolved solids entering the peritoneal cavity from the bags containing dialysis solution. According to United States Renal Data System (USRDS), there are 56% more deaths due to infection for patients using peritoneal dialysis therapy than for patients being treated using hemodialysis. According to the New England Journal of Medicine, peritonitis occurs once every 15 patient-months of dialysis. According to the USRDS some of the causes of peritonitis in CAPD patients are poor transfer technique, peritoneal access, less overall clearance of small uremic toxins, and possible deleterious effects of the dialysis fluid on the macrophage function.
A second problem associate with current CAPD procedures is the introduction of air into the peritoneal cavity. As the patient transfers fluid to and from the peritoneal cavity, air from the lines is flushed into the peritoneum. The air causes sharp pain in the shoulders and muscles of the patient until it is absorbed and removed. Depending upon the quantity of air, the pain can last from 20 minutes to several days. While air introduction is generally not life-threatening, it impacts significantly upon the quality of life of a dialysis patient.
Current technology relies upon the patient""s technique to prevent introduction of bacteria, organic matter and air into the peritoneum; however, even with proper technique every transfer exposes the peritoneum to the surrounding environment. The more transfers that are performed, the greater the number of exposures. According to the USRDS and the New England Journal of Medicine, however, increasing the number of transfers and the volume of fluid moved through the peritoneum correspondingly increases the effectiveness of toxin clearance.
A novel filter of this invention uses an absolute membrane micro-filter to screen out all bacteria and virtually all the organic matter. Currently, commercially available 0.2 micron absolute membrane filters are considered to be satisfactory, but it is recognized that other sizes and types of filter media will also be operable for the practice of this invention. In practice, the filter may be attached to an implanted catheter for an interval encompassing several transfers, using aseptic technique. It is generally convenient and sufficient to change filters once per day. Once the filter has been put in place, the patient is free to transfer solution virtually anywhere and in any situation. The filter provides a barrier between the environment and the peritoneal cavity, as well as a barrier between the non-dissolved solids in the dialysis solutions and the patient""s peritoneal cavity. It thereby addresses directly the causes of peritonitis. The effects of poor technique and the problems associated with peritoneal access are avoided to a great extent, because the patient need perform only one unprotected connection per several transfers (resulting in at least a 75% reduction in unprotected connections per day, assuming four transfers per day, using a single filter.) The filter may be sized to allow for five or more transfers per day to increase the toxin clearance. It maintains its protective properties throughout the day. It thus simply and efficiently eliminates the main problems associated with peritonitis.
The filter also eliminates the main cause of introduction of air into the peritoneal cavity. The first thing a patient does once the filter is attached is to drain the peritoneal cavity. The act of draining the peritoneal cavity primes the filter and effectively displaces any air in the filter between the patient and the filter membrane, including any air resident in the lines from the filter to the patient""s peritoneal cavity. The filter is ideally structured so that it primes in any position or orientation. The priming is thus unaffected by technique, and is accomplished every time the peritoneal cavity is drained. The filter membrane provides a barrier against the passage of air from between the dialysis solution bag and the filter membrane into the patient. An air vent may be provided on the solution bag side of the filter to allow the air from the lines to escape as the fresh solution moves through the filter to the peritoneal cavity.
The present invention provides a medical filter constructed as a chamber, having an interior openly communicating with a patient connection structure adapted for connection to a dialysis solution flow fixture carried by a dialysis patient. The interior is also in open communication with a transport connection adapted for connection to external dialysis solution containment apparatus, generally a supply of fresh dialysis solution or a disposal container for spent dialysis solution. Support structure, mounted within the interior, is usually structured as a thin, perforated member, having a relatively very large support surface. Hydrophilic filter medium is mounted atop the support surface, and has a pore size capable of separating particulate materials, including bacteria, from fresh dialysis solution. First channel structure within the chamber defines a first flow path from the patient connection across the surface of the filter medium to the transport connection. Second channel structure within the chamber defines a second flow path from the transport connection through the filter medium and the perforated support structure to the patient connection. Flow control mechanism may also be mounted within the chamber and operable to direct fluid from the patient connection through the first flow channel and to direct fluid from the transport connection through the second flow channel.
A presently preferred embodiment of the invention comprises a container with an interior volume in open fluid communication with a patient connection element and a transport connection element. Filter support structure is mounted within the interior volume. This structure may include a plurality of filter elements arranged in approximately parallel stacked arrangement, whereby to define a plurality of approximately parallel flow paths straddling the filter elements. Each filter element includes first and second panel members, each having an exterior surface and an interior surface. Apertures extend between those exterior and interior surfaces. First and second edge members connect the panel members at the respective interior surfaces of the panel members, whereby to enclose an interior fluid flow zone within the filter element The edge members have exterior and interior surfaces and carry ports arranged to permit liquid to pass through the first edge member, through the flow zone between the opposed edge members and out the second edge member. Hydrophilic filter medium is mounted to the exterior surfaces of the first and second panel members to cover the perforations. Flow control structure within the interior volume is constructed and arranged to: (1) cause liquid introduced through the patient connection structure to flow through the first edge member, through the flow zone, out the second edge member, and then across the exterior surfaces of the panel members to the transport connection element; and (2) cause liquid introduced through the transport connection member to flow into the interior volume to surround the filter elements, through the filter medium into the interior zone and out the ports in the first edge member to the patient connection structure.
The chamber may have an interior defined by a bottom portion and a cover portion. Visualizing the bottom portion as a box, the filter support structure is mounted within the interior. The filter support structure may be visualized as being formed from spaced, perforated top and bottom panel members, joined by perforated edge members to define a space constituting an interior flow path (or zone) between the panel members. The first channel structure within the chamber may be considered to include first and second segments structured and arranged so that liquid from the patient connection is directed by the first segment, through the perforated edge members and across the interior flow path to the second segment. The second channel structure within the chamber is structured and arranged to direct liquid from the transport connection, around the exterior of the support structure, through the filter medium into the interior zone and through the perforated edge members to the patient connection. A flow control mechanism mounted within the chamber may be structured and arranged to permit liquid flow from the second segment to the interior, thereby providing for washing of all surfaces of the filter medium. The bottom portion may conveniently take the form of a substantially rectilinear box, and the filter support structure may be oriented to hold sheets of filter medium approximately parallel the direction of flow of liquid traveling from the patient connection towards the transport connection.